Answer: To create a custom payment gateway in Concrete CMS, follow these steps:
1. Extend the Payment Method: Create a new PHP class that extends `ConcretePackageYourPackage srcPaymentMethod` to define your payment gateway.
2. Implement Required Methods: Override necessary methods, such as `getGatewayType()`, `initialize()`, `validate()`, and `processPayment()`.
3. Add Configuration Options: Use a form within your class to allow users to input their payment configurations (like API keys).
4. Handle Transactions: Implement the logic to handle payment processing through your gateway’s API in the `processPayment()` method.
5. Install and Configure: Deploy your package in Concrete CMS, and configure the payment method through the dashboard.
6. Test: Thoroughly test your gateway with sandbox/test credentials to ensure successful transaction processing.
This will allow you to incorporate a custom payment gateway into your Concrete CMS site.